Get Length of Linked List in DSA Python - Execution Trace

Concept Flow - Get Length of Linked List

Start at head node

↓

Is current node None?

Yes→Stop, length counted

No↓

Increment length count

↓

Move to next node

↩Back to check current node

Start from the head node, move through each node until the end, counting nodes one by one.

Execution Sample

DSA Python

def get_length(head):
    length = 0
    current = head
    while current is not None:
        length += 1
        current = current.next
    return length

Counts how many nodes are in the linked list by moving from head to end.

Execution Table

Step	Operation	Current Node	Length Count	Visual State
1	Start at head	Node(1)	0	1 -> 2 -> 3 -> None
2	Check current != None	Node(1)	0	1 -> 2 -> 3 -> None
3	Increment length	Node(1)	1	1 -> 2 -> 3 -> None
4	Move to next node	Node(2)	1	1 -> 2 -> 3 -> None
5	Check current != None	Node(2)	1	1 -> 2 -> 3 -> None
6	Increment length	Node(2)	2	1 -> 2 -> 3 -> None
7	Move to next node	Node(3)	2	1 -> 2 -> 3 -> None
8	Check current != None	Node(3)	2	1 -> 2 -> 3 -> None
9	Increment length	Node(3)	3	1 -> 2 -> 3 -> None
10	Move to next node	None	3	1 -> 2 -> 3 -> None
11	Check current != None	None	3	1 -> 2 -> 3 -> None
12	Stop and return length	None	3	1 -> 2 -> 3 -> None

💡 Current node is None, end of list reached, length counted as 3

Variable Tracker

Variable	Start	After Step 3	After Step 6	After Step 9	Final
length	0	1	2	3	3
current	Node(1)	Node(2)	Node(3)	None	None

Key Moments - 3 Insights

Why do we check if current is None before counting?

Because when current is None, it means we reached the end of the list and should stop counting. See execution_table steps 2, 5, 8, and 11.

Why do we move current to current.next after incrementing length?

We count the current node first, then move to the next node to continue counting. This order ensures no node is skipped. See execution_table steps 3 and 4.

What happens if the list is empty (head is None)?

The loop never runs because current is None at start, so length stays 0. See execution_table step 11 where current is None and loop stops immediately.

Visual Quiz - 3 Questions

Look at the execution_table, what is the length count after step 6?

A 1

B 3

C 2

D 0

💡 Hint

Check the 'Length Count' column at step 6 in the execution_table.

At which step does the current node become None?

A Step 9

B Step 10

C Step 11

D Step 12

💡 Hint

Look at the 'Current Node' column to find when it changes to None.

If the linked list had 5 nodes instead of 3, how many times would length increment?

A 5

B 4

C 3

D 6

💡 Hint

Length increments once per node, so check variable_tracker for length increments.

Concept Snapshot

Get Length of Linked List:
- Start at head node
- While current node is not None:
  - Increase count by 1
  - Move to next node
- Return count as length
Simple traversal counting nodes until end.

Full Transcript

To get the length of a linked list, start at the head node and move through each node one by one. For each node, increase a count by one. When you reach a node that points to None, it means the list ended. The count at this point is the length of the list. If the list is empty, the count stays zero. This method uses a simple loop checking if the current node exists, counting it, then moving to the next node until the end.